Perforations in ceiling tiles give them a special appearance that we’ve come to associate with their unique look. If you’ve ever studied them more closely, you might have wondered about the holes punched into the ceiling tiles. Too many to count, they all seem placed in random spots with no rhyme or reason. So, why are ceiling tiles perforated?
The holes in ceiling tiles serve a fundamental purpose: to absorb sound waves and reduce the amount of noise in a room. Perforated ceiling tiles are commonly known as acoustic ceiling tiles. You will often find them installed in places like schools, offices, conference rooms, and sometimes in homes.
In this article, we’ll take a look at acoustical tiles, including how they are installed, what purposes they serve, and how they work. This article will reveal the three primary ways in which the performance of acoustical ceiling tiles is rated and how effective they are when it comes to reducing unwanted noise in a room.
What Are Acoustical Ceiling Tiles?
Acoustical ceiling tiles are specialized ceiling tiles that are designed to reduce noise in a room. They are typically manufactured from fiberglass, acoustical foam, polyester, or other sound-reducing materials. They are designed to fit seamlessly in dropped ceilings (aka T-bar, floating, or suspended ceiling) grids and support systems. They can also be installed directly on an existing ceiling if a dropped ceiling is not an option. (Source: Acoustical Solutions)
Here’s How They Work
Sound is caused by vibrations occurring at the sound source and travels by causing molecules that are adjacent to each other and move back and forth, one after the other. As this series of molecule-shaking continues, sound moves away from the sound source in all directions in the form of sound waves. It is when these waves hit your eardrum that your brain processes them as audible sound. (Source: OpenLearn)
When sound waves encounter an object in their path, they typically do one of three things:
- They can be absorbed by the object.
- They can pass through the object.
- They can bounce, or deflect, off the object.
In the case of sound waves in a room, an acoustical ceiling tile is designed to absorb them and prevent them from bouncing around the room. The holes (also known as perforations) in acoustical ceiling tiles increase the amount of tile surface area and trap sound waves within them. Vibrations in the sound waves are absorbed by the perforations and dissipated through the ceiling tile material. (Source: Ask the Builder)
Aside from absorbing sound waves within a room, acoustical ceiling tiles can also serve other purposes:
- They can help prevent sound from traveling from one room to an adjacent room. This is beneficial in an office or school setting where privacy or confidentiality concerns may exist. Acoustical ceilings tiles can absorb or block sound waves to the point that voices are muffled, and words are unintelligible from one room to another.
- Another scenario where acoustical ceiling tiles are beneficial is in sound reduction between rooms that are above and below each other. Perhaps your college grad has moved back in with you, and there is now an immediate need to reduce the amount of noise coming up from your basement into the living room. Acoustical ceiling tiles are an excellent place to start in your quest for some quiet.
How Are Acoustical Ceiling Tiles Rated?
Selecting the right acoustical ceiling tiles for your sound reduction needs can be a daunting task if you are not a contractor or ceiling expert. Fortunately, there are rating systems that provide a numerical value that corresponds to an acoustical ceiling tile’s effectiveness in reducing noise within specific parameters.
The following sound reduction scores can guide you to the right tiles for your particular needs:
- Noise Reduction Coefficient (NRC) – This is a rating that indicates the sound absorption capability of an acoustical ceiling tile. It is typically expressed as a percentage, with a higher value corresponding to a greater reduction of noise through absorption. NRC is an indication of a tile’s ability to reduce sound traveling within a particular enclosed space, such as a room.
For example, an NRC rating of 65 means that the tile in question can be expected to absorb 65% of the sound waves that hit its surface. However, while 65% of the sound will be absorbed, the other 35% will be reflected by the ceiling tile, meaning it will reflect from the tile and travel around the room. (Other NRC rating systems utilize a decimal system where 0 is no absorption and 1 is perfect absorption.)
A typical application of acoustical ceiling tiles with high NRC ratings is to reduce the amount of echo or unwanted noise in a room. Tiles used for this purpose fall in the sound absorption category.
- Sound Transmission Class (STC) – The STC rating of an acoustical ceiling tile indicates its ability to block sound waves from passing through its structure. As with NRC, this rating is numerically assigned, with the higher value indicating a more exceptional ability to block sound. STC is commonly considered when the direction of sound travel in question is up and down, as in enclosed spaces that are directly above and below each other.
Tiles designed for this application are known as sound-blocking acoustical tiles. Since the goal is sound blocking (and not absorption), the sound waves are still bouncing around the room in the form of echoes, so other sound absorption measures will need to be taken (e.g., sound-absorbing walls, carpet, drapes, furniture).
In general, acoustical ceiling tiles with STC ratings of 60 or higher (some STC rating systems go higher than 100) are considered very good when it comes to blocking sound waves. On the flip side, if you see an STC rating of 10 or below, you can expect that your conversations will travel through the ceiling tiles and be heard on the other side.
- Ceiling Attenuation Class (CAC) – Acoustical ceiling tiles that have been tested for Ceiling Attenuation Class and have been assigned a CAC rating are designed to inhibit sound from traveling from one room to an adjacent room, where the two rooms share air space above their ceilings.
More specifically, CAC-rated ceiling tiles are used with drop ceiling systems, where the walls only rise to the level of the suspended grid that supports the tiles. The idea behind these specialized acoustical tiles is to prevent sound from traveling from the room below, into the space above the ceiling, and down into the adjacent room.
CAC ratings matter when considering acoustical ceiling tiles for installation in places like schools and office buildings, where there are numerous adjoining rooms and dropped ceiling systems are heavily used. Without measures in place such as ceiling tiles with high CAC ratings, conversations can be heard from one room to another.
There are times when noise reduction is not only desirable but absolutely necessary. Trying to have a conversation while words are echoing around the room and keeping a confidential discussion private are but a few scenarios where acoustical ceiling tiles can substantially reduce, block, or diffuse sound.
Acoustic ceiling tiles also help reduce noise from traveling between floors. While there are other materials and techniques which can be more effective at minimizing sound, perforations in acoustic tiles are an inexpensive and reasonably effective way to reduce noise, while softening the echo effect caused by acoustic reverberation.